1. Field of the Invention
The present invention relates to an ion-conductive polymer electrolyte and an aluminum electrolytic capacitor configured with the same electrolyte as an electrolyte for driving the electrolytic capacitor.
2. Description of the Prior Art
Conventionally, as an electrolyte for driving an aluminum electrolytic capacitor, a solution prepared by dissolving an ammonium salt in an organic solvent having a high dielectric constant such as ethylene glycol has been used. However, because of possible leakage and evaporation of the electrolyte, it has been impossible to obtain a long-lasting reliable operation in the capacitor using such liquid electrolyte.
In order to solve these problems, there has been proposed an electrolytic capacitor that is free from the leakage and evaporation of the electrolyte. Such a capacitor is configured by solidifying the capacitor element with the use of an ion-conductive polymer electrolyte composed of a mixture of siloxane-alkylene oxide copolymer and polyethylene oxide, as its prepolymer, and an alkali metal salt, instead of the liquid electrolyte.
However, the electrolytic capacitor using, as its electrolyte, the ion-conductive polymer electrolyte in which alkali metal ions serve as the mobile ions has a disadvantage that the alkali metal ions are liable to diffuse into a dielectric substance layer formed on a positive electrode of the electrolytic capacitor, and the thus diffused alkali metal ions might sometimes cause a lowering of the dielectric constant of the dielectric substance layer, and finally invite a short-circuit in the capacitor.
In order to overcome such disadvantage, it has been considered to use ammonium ions in place of the alkali metal ions which had been used as the mobile ions of the electrolyte constituting the electrolytic capacitor. However, it has hitherto been known that the ion-conductive polymer electrolyte which contains ammonium ions has a very poor ionic conductivity in general.
The ionic conductivity of the electrolyte constituting the electrolytic capacitor acts as an impedance of the capacitor. Therefore, when the ionic conductivity of the electrolyte is too poor, the impedance of the capacitor increases and such a capacitor is difficult to use in practical point of view.
In order to enable an employment of such ion-conductive polymer electrolyte as the electrolyte for driving an electrolytic capacitor, it is essential to clarify a suitable combination of various polymer mother ingredients (prepolymers) with ammonium salts for realizing an electrolyte of high ionic conductivity, but no concrete example has been clarified.
In addition, application of the aluminum electrolytic capacitor has recently been expanded widely, and the importance of its long-term reliability after a storage at a high temperature has been attracting attention. For instance, a guaranteed quality after a continuous exposure to a high temperature of 105.degree. C. for 10,000 hours is now required by the current market. When the polymer electrolytes are exposed to such high temperature atmosphere, physical and/or chemical deterioration such as crack, contraction or dissolution (liquefaction) may be produced, and thus the exposure may cause a serious deterioration in the characteristics of the capacitor element. A solid phase electrolyte which does not suffer from any deteriorated performance due to such severe test environments has not so far been proposed.